python异步编程asyncio实现协程

import asyncio
@asyncio.coroutine
def f1():
    print(1)
    yield from asyncio.sleep(2)
    print(2)

@asyncio.coroutine
def f2():
    print(3)
    yield from asyncio.sleep(2)
    print(4)

tasks=[
    asyncio.ensure_future(f1()),
    asyncio.ensure_future(f2())
]
loop=asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(tasks))